Precise location of a target is essential for reducing the morbidity rate during a surgical operation involving cerebral tumour ablation. During a surgical operation on the brain, a shift in cerebral tissues (or “brain shift” according to English terminology) can occur after an opening has been made in the cranium of the patient. This shift can be associated with physical phenomena (gravity, loss of cephalorachidian liquid, action by the neurosurgeon, etc.) or with physiological phenomena (tumefaction due to osmotic, anaesthetic drugs, etc.), some of which are still unknown.
Neuro-navigation systems have been developed to compensate for this brain shift of the patient and discover the preoperative data of the patient during the surgical procedure. These neuro-navigation systems display the position of surgical objects relative to the position of the anatomical cerebral characteristics of the patient for the surgeon. In this type of system the compensation of the brain shift of the patient is generally made on the following principle.
A first image of the cortical surface of the patient is acquired prior to the surgical operation. During the surgical operation, a second image of the cortical surface of the patient is acquired. Processing means of the system compare these two images and estimate a shift volume field which enables the points in the two images to be aligned to compensate for the brain shift of the patient. Such systems are especially described in documents U.S. Pat. No. 7,072,705 and U.S. Patent Publication No. 2007/0021669.
Yet, a disadvantage of this compensation technique of the brain shift of the patient from points of the cortical surface is that it leaves out a significant zone of the brain (under the cortical surface) in which the real brain shift is unknown. An aim of the present invention is to propose a system and a compensation process of the brain shift of the patient for rectifying at least one of the above disadvantages.